Fatigue indicator

Abstract

The invention relates to a fatigue indicator for mechanical parts subjected to repeated stresses, which comprises two thick elements spaced apart from one another and joined together by a thin web having a slit, these two elements being incorporated in the part or fixed thereto so as to move with respect to one another upon application of stress on the mechanical part in a plane which is parallel to the plane of the web, the thin web being thus subjected to a shearing stress in its plane, and wherein the slit of the thin web extends from one of the edges of the web in the direction of relative movement to a blind end so that, when the part is stressed, two cracks appear from corners of the blind end of the slit, extend progressively in the web and finish by reaching the opposite edge of the web or joining cracks coming from this opposite edge, the web thus being detached or practically detached.

What I claim is: 
     
       1. In a fatigue indicator for a mechanical member subjected to repetitive stress, comprising an elongated flat body formed with a pair of elongated thick elements spaced apart from one another across a longitudinal axis of said body and connected to each other by at least one thin web formed with a slot and having a pair of free opposite edges, the pair of thick elements being so joined with the mechanical member that said elements are displaceable relative to one another in a plane parallel to the plane of the web by stress applied to said member, the web being subjected to shear force in its plane by the relative displacement of said elements, the slot of said web extending parallel to said axis from one of the edges of said web and terminating short of the opposite edge in a blind end having two corners whereby with application of said stress to the member, two cracks develop at said corners of the end of said slot and are propagated progressively in the web towards an opposite edge thereof so that said cracks meet other cracks propagating generally in a direction away from said opposite edge to substantially sever said web, the improvement wherein said pair of thick elements are joined at each of their respective ends to respective intermediate portions by a first flexible zone offset from said axis, each respective intermediate portion being joined to said mechanical member to be montiored by a second flexible zone offset from said axis.   
     
     
       2. The improvement defined in claim 1, wherein each of said second flexible zones is disposed on an opposite side of said axis. 
     
     
       3. The improvement defined in claim 2, wherein said second flexible zones are offset from said axis by a distance greater than the offset of said first flexible zones. 
     
     
       4. The improvement defined in claim 2, wherein said second flexible zones are offset from said axis by a distance less than the offset of said first flexible zones.